Hopefully you already know, but tonight’s kind of a big deal. A not-since-1982-have-we-had-a-full-moon-this-rare kind of big deal. And in anticipation of this Supermoon Lunar Eclipse, NASA Goddard put together an animated primer to explain exactly why this is such a special occurrence.

Yep, you miss tonight and the next “tetrad” as it’s called isn’t until April 25, 2032.

Still don’t get it? The Inertia Contributing Editor Dashel Pierson breaks it down:

Full Moon

Ok, you know this one. It’s when the tides fluctuate drastically and werewolves come out to play. It’s also when the moon is fully exposed to the sun, making the near side of it completely illuminated.

Lunar Eclipse

This one is a little tougher to grasp. A lunar eclipse is when the moon passes directly behind the earth’s shadow. It can only occur during a full moon and it makes the appearance of the moon a creepy shade of red, hence the name “Blood Moon.” Many ancient cultures believed that lunar eclipses were the result of demons swallowing the moon; and even today, Blood Moons give people the heebie jeebies.

Lunar Perigee

Don’t freak out. This is the most complex aspect of Sunday’s full moon, but you don’t have to be Neil deGrasse Tyson to comprehend it. The moon rotates around the earth on a lopsided axis. Because it isn’t a perfect circle, there are points when the moon is closer to earth than others. These points are called perigee (closest) and apogee (furthest). Since the moon appears larger in the perigee position, it’s often called a “Supermoon.”